We will investigate the detailed mode of mitochondrial DNA replication in malignant mouse and human cells. These cell lines exclusively label mitochondrial DNA since they have lost the soluble cytoplasmic thymidine kinase but retain a mitochodrial thymidine kinase. These studies will involve an examination of the molecular structure of replicating molecules, the rate of mitochondrial DNA biosynthesis as a function of cell growth parameters, the effect of deoxyribonucleotide analogues (which are anti-cancer drugs) on mitochondrial DNA replication and subsequent transcription and protein synthesis, and a search for the gene protein products of mitochondrial DNA. The results with these special cell lines will be compared with mitochondria from human leukemic leukocytes in order to better understand the role of circular dimer mitochondrial DNA in human cancer. Our cell lines contain a variety of complex mitochondrial DNA forms which allows us to study the biosynthesis of each form independently. Completion of these studies should lead to an understanding of the role of mitochondrial nucleic acids in the neoplastic process.